1. Field of the Invention
This invention relates to a papermaking chemical, a method for manufacturing this papermaking chemical, and paper containing the same, and more particularly relates to a papermaking chemical exhibiting an excellent paper strengthening effect, drainage improvement effect, retention improvement effect, plybond strength enhancing effect, surface strength enhancing effect, and sizing improvement effect in acid, neutral, or alkaline papermaking systems; a method for manufacturing a papermaking chemical containing a (meth)acrylamide polymer, with which this papemiaking chemical can be formed; and paper that makes use of this (meth)acrylamide polymer and as a result has excellent bursting strength, internal bond strength, and other such properties.
2. Background Art
Various kinds of papermaking chemicals have been used in the papermaking process in the past for the purpose of raising productivity through higher machinery speed, or improving the paper quality. (Meth)acrylamide polymers are especially important chemicals in terms of improving paper quality and raising productivity, and as such these chemicals are being used in an increasingly wide range of applications and continue to be improved.
(Meth)acrylamide polymers are widely used as papermaking chemicals having a paper strengthening effect, drainage improvement effect, retention improvement effect, plybond strength enhancing effect, surface strength enhancing effect, sizing improvement effect, and so forth. From the standpoint of their ionicity, (meth)acrylamide polymers are classified into anionic, cationic, and amphoteric polymers. At first, anionic (meth)acrylamide polymers were used along with aluminum sulfate back in the 1960's. Then, in the 1970's and 80's, Mannich-modified (meth)acrylamide polymers, Hofmann-modified (meth)acrylamide polymers, and other such polymers into which cationic groups had been introduced came into use for the purpose of improving drainage and retention. However, aqueous solutions of these modified (meth)acrylamide polymers have poor viscosity stability. Also, a problem with a Mannich-modified (meth)acrylamide polymer aqueous solution is that it contains formalin.
Then, beginning in the 1980's, an amphoteric (meth)acrylamide polymer produced by copolymerizing acrylamide with an anionic vinyl compound and a cationic vinyl compound came into use (see Japanese Laid-Open Patent Application S60-94697, etc.). This amphoteric (meth)acrylamide polymer is used alone or together with an anionic (meth)acrylamide polymer.
Researchers have also improved the polymerization method in an effort to increase the effectiveness of a (meth)acrylamide polymer as a papermaking chemical. Some documents disclose a method for enhancing performance by continuously synthesizing an anionic (meth)acrylamide polymer and a cationic (meth)acrylamide polymer by two-stage dropping polymerization, thereby forming a so-called ion complex (see Japanese Laid-Open Patent Applications H6-199965 and H7-90797, for example). However, obtaining a satisfactory effect with a papermaking chemical containing a conventional (meth)acrylamide polymer has become impossible in recent years because of fluctuation in the pulp slurry pH during papermaking as a result of variance in the quality of the papermaking raw material, or because of increases in the amount of recycled paper being used, that of the admixed impurities due to the fact that the papermaking process has become a more closed system, that of fines, and so forth. Under these circumstances, there is a need for further improvement to papermaking chemicals in order to increase productivity, paper strength, sizing, and so on.
Compounds for obtaining a polymer with good fluidity and dispersibility and low viscosity have also been proposed in an attempt to raise the productivity of (meth)acrylamide polymers and to improve the effectiveness of (meth)acrylamide polymers as papermaking chemicals. These compounds include 2-propanol, hypophosphorous acid, mercaptans, all of which compounds are known chain transfer agents. In addition, 2-propen-1-ol (that is, allyl alcohol), 2-methyl-2-propen-1-ol (that is, methallyl alcohol) (Japanese Laid-Open Patent Application H8-283341), 2-propene-1-sulfonic acid (salt) (that is, allylsulfonic acid (salt)), 2-methyl-2-propene-1-sulfonic acid (salt) (that is, methallylsulfonic acid (salt)) (see Japanese Laid-Open Patent Applications H8-67715, H8-176990, H8-269891, H8-283341, and H8-333427, for example), and 2-methyl-2-propenenitrile (that is, methacrylonitrile) (Japanese Laid-Open Patent Applications 2000-212229 and 2000-273387) are known as monomers having the function of lowering the viscosity of a polymer, but most of these are nonionic or anionic.
Examples of cationic monomers having the function of lowering the viscosity of a polymer include 2-propenylamine (that is, allylamine) and 2-methyl-2-propenylamine (that is, methallylamine), but these alone will not adequately lower the viscosity of a polymer. Therefore they are used together with a chain transfer agent in actual practice. For instance, when 2-propenylamine is used, 2-methyl-2-propene-1-sulfonic acid (salt) is used to lower the viscosity of the polymer (see Japanese Laid-Open Patent Application H11-217792, for example). Conversely, if an attempt is made to lower the viscosity of a polymer with one of the above by itself, the compound has to be used in a large quantity, in which case the problem is that a large amount of unreacted monomer remains behind.
Thus, from the standpoint of the ionicity of a compound having the function of lowering the viscosity of a polymer, none of the options is satisfactory. It has become difficult to achieve the above-mentioned high level of performance as a papermaking chemical and to deal with the increasing demands of papermaking conditions.
There has recently been proposed a method for manufacturing a (meth)acrylamide polymer with low viscosity and good fluidity and dispersibility by polymerizing a monomer aqueous solution whose main component is (meth)acrylamide and which contains 2-methyl-2-propenylamine (that is, methallylamine), an inorganic acid or organic acid salt of 2-methyl-2-propenylamine, or a 2-methyl-2-propenyl ammonium salt obtained by reacting methyl chloride, benzyl chloride, epichlorohydrin, or dimethylsulfuric acid with 2-methyl-2-propenylamine (Japanese Laid-Open Patent Applications H8-283341 and H8-333427), but it has not been known that a cationic monomer such as that defined by general formula 1 of the present invention has the function of lowering the viscosity of a polymer.
It is an object of the present invention to provide a papermaking chemical that makes use of a cationic monomer having the function of lowering the viscosity of a polymer and that has an excellent paper strengthening effect, drainage improvement effect, retention improvement effect, plybond strength enhancing effect, and surface strength enhancing effect, and particularly its sizing improvement effect, as well as paper containing this papermaking chemical, a (meth)acrylamide polymer that is favorable for constituting this papermaking chemical, and a method for manufacturing this (meth)acrylamide polymer.